The Fall equinox

When and why does it happen?

The seasons of the year are caused by the 23.5º tilt of the earth's axis.
Because the earth is rotating like a top or gyroscope, it points in a fixed
direction continuously -- towards a point in space near the North Star. But the
earth is also revolving around the sun. During half of the year, the southern
hemisphere is more exposed to the sun than is the northern hemisphere. During
the rest of the year, the reverse is true. At noontime in the Northern
Hemisphere the sun appears high in the sky during summertime and low in the sky
during winter. It is highest at the summer solstice (about June-21) and lowest
at the winter solstice (about December-21). The half-way points in the
year are called
the equinoxes. It is time of the year when the sun rises exactly in the east,
travels through the sky for 12 hours, and sets exactly in the west.
1,2 Everywhere on earth experiences close to 12 hours of daylight,
and 12 hours of nighttime.

The exact date and time of the fall equinox, when the sun moves into the
astrological sign of Libra, varies from year to year. Each year, the date/time
moves progressively later in September until the year before leap-year is reached.
On leap-year, it returns to an earlier date/time. This four-year cycle is then
repeated.

Year

Fall Equinox,
in the Northern Hemisphere
(UT)

1999

SEP-23 @ 11:32

2000

SEP-22 @ 17:27

2001

SEP-22 @ 23:04

2002

SEP-23 @ 04:55

2003

SEP-23 @ 10:46

2004

SEP-22 @ 16:29

2005

SEP-22 @ 22:22

2006

SEP-23 @ 04:03

2007

SEP-23 @ 09:51

2008

SEP-22 @ 15:44

2009

SEP-22 @ 21:18

2010

SEP-23 @ 03:09

2011

SEP-23 @ 09:05

2012

SEP-22 @ 14:49

2013

SEP-22 @ 20.44

2014

SEP-23 @ 02:29

2015

SEP-23 @ 08:20

2016

SEP-22 @ 14:21

The dates and times were derived from the astronomical calculations on
The Dome of the Sky web site for years 1999 to 2006. 3
However, the web site now appears to be offline. The
remaining equinoxes were taken from archaeoastronomy.com. 4 An
online "Easy Date Converter" calculates the dates and times of the
equinoxes and solstices within 20 seconds. 5 Times are
in UT (Universal Time). This used to be called Greenwich Mean Time or GMT. In
North America, you can find your local time by subtracting:

2 hours 30 minutes for Newfoundland daylight savings time

3 hours for ADT

4 hours for EDT

5 hours for CDT

6 hours for MDT

7 hours for PDT

8 hours in AKDT (Alaska)

9 hours in ADT (Aleutian Islands)

10 hours in HST (Paradise, a.k.a. Hawaii) 6

Sponsored link:

References used:

The following information sources were used to prepare and update the above
essay. The hyperlinks are not necessarily still active today.

"Dates and Times of Equinoxes, Solstices, and Cross Quarter days," Hermetic Systems,
at: http://www.hermetic.ch They have a free trial program that works on years ending in "9." They sell a fully functional program for under US $10.00.

Actually, this is not precisely true. The Earth wobbles like a decelerating top and completes one cycle in about 25,765 years. The interval of time is called a "Great Year" or "Platonic Year." This motion is called "precession of the equinoxes:" As a result, the star to which the North Pole points changes down through the millennia. More details: